Advances in integrated circuit architecture and miniaturization have resulted in greater numbers of functions being incorporated on single chips, necessitating the use of chips with larger dimensions, increased lead density and/or reduced lead pitch. Fine pitch integrated circuit devices may have lead pitches (center-to-center spacing between leads) of 0.006 to 0.010 inch. For example, one package of the Pentium microprocessor has 322 leads. It is expected that integrated circuits will soon have up to 1,000 leads. The device must be aligned with a pattern of conductive pads on the printed circuit board to accuracies within 0.001 to 0.002 inch. A proposed integrated circuit package known as "flip chip" uses a pattern of ball contacts on the back surface of the integrated circuit package as input/output leads. The ball contacts may have diameters of 0.004 inch and a pitch of 0.008 inch. The ball contacts may cover all or a major portion of the rear surface of the integrated circuit package. Placement of the flip chip package on a printed circuit board is particularly difficult, because the ball contacts cannot be seen when the device is placed on the board.
Systems have been developed for automatic placement of integrated circuits on circuit boards. The trend in integrated circuit packaging to increased numbers of leads and decreased lead pitches, as well as the development of new integrated circuit packaging techniques, has imposed increased demands on integrated circuit placement systems. The need for increased accuracy has increased the cost of placement systems. Some prior art systems are unable to meet the placement requirements for newer integrated circuit packages.
A guidance-type placement apparatus, including an image acquisition/processing subsystem, for placing and mounting integrated circuit components or devices is disclosed in U.S. Pat. No. 5,235,407 issued Aug. 10, 1993 to Spigarelli et al. In the disclosed system, the image acquisition subsystem generates images of at least one pair of diagonally-opposed corners of the placement site and the IC device from the same optical perspective. Images generated by the image acquisition system provide feedback control to regulate the placement process to attain and verify lead-to-pad alignment.